Phase equilibria of Cu-In-Se I. Stable states and nonequilibrium states of the In2Se3-Cu2Se subsystem

In three subsequent publications we report new results on the phase equilibria of Cu-In-Se, obtained by analysing more than 250 alloys with a variety of experimental methods. This part, part I, deals with the isopleth In2Se3-Cu2Se obtained by analysing more than 70 alloys. The experimental results, including an isothermal section at 500°C that ranges from 0 to 45 at.% Cu and from 40 to 70 at.% Se, support the hypothesis that the In2Se3-Cu2Se isopleth constitutes a 'quasibinary' section. It includes 10 critical tie lines. Depending on the processing conditions, not only stable phases but also nonequilibrium phases were observed to form in this section. In particular, this holds true for the α phase (CuInSe2), a semiconductor with promising properties for application in thin-film solar cells: By adequate heat treatment one can substantially broaden the compositional range of this technologically important phase.